In an internal combustion engine such as an automobile engine, measures such as making fuel lean and highly supercharging air are required in order to reduce environmental load substances and improve fuel efficiency. As an ignition device having a higher ignitability, a high-frequency plasma ignition device has been developed in which, after trigger discharge by a spark plug, high-frequency current is applied to obtain a plasma state at high temperature and high pressure to perform ignition.
In a high-frequency plasma ignition device composed of a battery, a full-bridge inverter, a transformer, a resonant circuit, a spark plug, and a high-voltage circuit, it is disclosed that arms in an inverter circuit are shared so that the number of arms becomes less than twice the number of spark plugs (for example, Patent Document 1). In addition, a switching power supply is disclosed in which a snubber circuit is provided for protecting a switching element from surge voltage occurring at the time of switching, a clamp diode is provided between the switching element and an inductor, and energy stored in a capacitor is regenerated to the power supply (for example, Patent Document 2).